The present invention relates generally to optical devices having resistance to laser damage, and more particularly to a thin film structure and method for making same having enhanced resistance to damage by laser irradiation.
Laser resistant structures comprising optical switching materials are well developed for applications such as laser output couplers, optical filters, modulators and the like. A typical switching material transitions from substantial transparency characteristic of a non-metallic (semiconductor) insulating phase below a characteristic transition temperature to substantial opacity characteristic of a metallic conducting phase above that temperature over a broad range of wavelengths.
Vanadium dioxide (VO.sub.2) switches upon being heated to about 68.degree. C. from the monoclinic structure to the tetragonal structure, with concurrent significant changes in electrical and optical properties which render the material highly useful in laser power limiting devices. However, thin VO.sub.2 films or layers in existing devices have an undesirably low damage threshold, and may experience failure through film delamination, substrate damage or film meltdown under very high energy density exposure. Structures incorporating VO.sub.2 films having enhanced damage resistance are therefore needed.
The invention provides a thin film structure and method for making same having enhanced resistance to damage from invasive high energy laser radiation as compared to structures prepared conventionally. A structure according to the invention a film of optical switching material deposited onto a lattice matched substrate. Selective substrate surface preparation according to an aspect of the invention further enhances damage resistance of the deposited film.
It is therefore a principal object of the invention to provide a film structure which is resistant to damage from invasive laser radiation.
It is a further object of the invention to provide method for fabricating a laser damage resistant structure.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.